Heat activated absorption cycles, using a wide variety of working fluids, have been utilized to provide cooling, refrigeration, and heating for many years. Absorption cycles utilize heat energy as the primary energy source, instead of mechanical work (most commonly using electric motors) utilized by vapor-compression heat pump cycles. The most common working fluids for absorption cycles are ammonia-water (NH3—H2O) and lithium bromide-water (LiBr—H2O), although there are many other suitable combinations. Since water is used as the refrigerant for LiBr—H2O systems, LiBr—H2O cycles are applicable for cooling, but cannot be used for heat pump applications.
An absorption heat pump transfers low grade (low temperature) heat and ‘pumps’ it up to a higher, more useful temperature, using a higher grade energy source (combustion, solar, or waste heat for example). The resulting cycle coefficient of performance (COP) is greater than 1.0 (typically 1.5 to 2.0) depending upon the cycle and temperatures involved. In a domestic water heating application, the low grade heat energy source can be indoor or outdoor ambient air (although other sources such as geothermal can also be used), and water is heated from typical ground temperatures (approximately 50° F.) to 100 to 160° F.
Electrically driven heat pump water heaters are commercially available; which have a COP of approximately 2.0. However, on a primary fuel basis, the COP is actually about 0.7, since electrical power is typically produced at an approximate 35% efficiency. The proposed invention provides significantly higher primary fuel COP of approximately 1.5, cutting CO2 emissions in half compared to electric heat pump water heaters. Commercially available conventional gas-fired water heaters have primary fuel COP ranging from about 0.6 to about 0.82.
One historical problem with absorption equipment, which requires many heat exchangers and at least one pump, is high manufacturing cost. Therefore, the need exists for an economically feasible absorption heat pump system.